Pituitary Adenylate Cyclase Activating Polypeptide (PACAP), as a small peptide with either 38 amino acids in full length form (PACAP-38), or 27 amino acids in short form (PACAP-27), is broadly recognized as a neurotrophin associated with stress. Both forms strongly increase cyclic adenosine monophosphate (cAMP) by activating adenylate cyclase, and hence named as PACAP. Subsequent research showed that PACAP is not only an endocrine hormone, but intrinsically expressed in multiple brain regions and peripheral tissues. PACAP is a potent neurotrophic and neuroprotective peptide in the central nervous system (CNS). PACAP-38 is the major form in brain, while PACAP-27 exists in minor quantity. Both forms of PACAP bind to and activate G protein-coupled receptors (PAC1, VPAC1, and VPAC2). PAC1 is mainly localized in the CNS; while VPAC1 and VPAC2 are in the vascular system and the gastrointestinal tract.
PACAP has been shown to promote synaptic transmission, long term potentiation and memory under physiological conditions. However, the relevance of PACAP expression has not been extensively studied in the human brain, including those suffering from Alzheimer's disease (AD), a progressive mental deterioration and form of dementia that often occurs in old age due to generalized degeneration of the brain. AD is a neurodegenerative disorder that affects memory and other cognitive functions, and is the most common cause of dementia. Alzheimer's Disease Association (ADA) survey shows that 5.4 million people in the United States (US) currently have AD and 13.5 million are expected to have AD within the next 40 years. AD affects over 26 million people worldwide and currently there is no cure for the disease. With the growing number of people living to older ages, there is an urgency to better understand elements of the pathogenic pathway, discover agents that target these elements, and establish their roles in the treatment and prevention of AD. But effective biomarkers and treatment are lacking. There is no disease modifying medication available on the market.
Thus, there is a need in the art for novel and effective treatments and methods of diagnosing Alzheimer's disease and other forms of dementia.